Changes in microtubule arrays during cotton fiber development
Developing cotton fiber provides an excellent model system for the study of microtubule (MT) arrays and their involvement in cell wall deposition. The secondary wall of the cotton fiber is arranged in layers of parallel microfibrils, to produce a polylamellate configuration. Cortical MTs parallel microfibrils and undergo re-orientations which predicted new microfibril orientations. Previous studies describe the general relationship between MTs and microfibrils but provided no quantitative analysis of MT arrays. In this paper quantitative measurements of MT arrays were done during primary and secondary wall synthesis. Changes in the MT array accompany the shift from primary to secondary wall deposition.Fibers of cotton (Gossypium hirsutum, variety Acala SJ-2) were grown using ovule culture techniques. At various stages of development (days post anthesis, DPA) ovules with attached fibers were fixed in 0.1M phosphate buffered (pH 6.9) 1% glutaraldehyde for 1 h. After a 1 h wash, the fibers were post-fixed in phosphate buffered 1% OsO4. After rapid dehydration with 2,2 dimethoxypropane, cells were infiltrated with Spurr's resin. At this point fibers were removed from ovules and flat embedded between teflon coated microscope slides. Serial section reconstruction analysis of microtubule arrays was done as previously described.